859 LOCUST ST 2022-07-20 - Laserfiche WebLink

WC:1 Minimum Requirement#2: Stormwater Pollution Prevention Plan A SWPPP has been prepared for this project. Erosion control best management practices(BMPs) which fulfill the minimum erosion control requirements outlined by the Department of Ecology will be installed and maintained during the construction. The twelve elements of the SWPPP are summarized in Section 6 of this report. Minimum Requirement#3: Source Control of Pollution All applicable source control BMPs have been considered for use on the project site.All applicable maintenance BMPs will be included in ongoing use of the site. Minimum Requirement#4: Preservation of Natural Drainage Systems and Outfalls As there appears to be no natural drainage systems near the project site, the existing underground conveyance system shall be utilized. Existing drainage patterns on-site include flow toward the west where drainage will flow into existing structures connection to the existing combined sewer system.Stormwater runoff from the improvements will be given the opportunity to infiltrate within the rain garden on site. Overflow from the rain garden will discharge at pre-developed rates to the existing combined sewer system just north of the proposed clubhouse. Minimum Requirement#5: On-Site Stormwater Management BMP T5.13 — Post Construction Soil Quality and Depth will be provided to infiltrate, disperse, and retain stormwater runoff on-site to the maximum extent feasible without causing flooding or erosion impacts. Minimum Requirement#6: Runoff Treatment The stormwater runoff generated by new impervious surfaces resulting from the Grandview Apartments clubhouse improvements will be treated through the physical,chemical,and biological processes provided by the proposed rain garden. Minimum Requirement#7: Flow Control Flow control will be provided by rain garden proposed to be located west of the proposed clubhouse. The drainage from the parking lot and clubhouse rood will be routed to the rain garden providing an opportunity infiltration. Water will be detained within the rain garden until soils are over-saturated at which point the drainage will be conveyed from the underdrain to the combined sewer. An overflow riser shall be installed in the rain garden as well at which upon reaching the overflow elevation, stormwater will also flow into the combined sewer. Minimum Requirement#8: Wetlands Protection There are no wetlands within the proximity of this project. Therefore, this requirement does not apply to this project. DAVID EVANS AND ASSOCIATES,INC. GRANDVIEW APARTMENTS CLUBHOUSE MARCH,2017 STORMWATER SITE PLAN PAGE 3